Many buildings, construction sites, manufacturing plants and machine shops require or use a significant quantity of bent tubes, pipes and rods to produce items such as hand rails, scaffolding, or fabricated metal products. A variety of conventional machines have been developed to facilitate the otherwise difficult task of bending of rigid metal tube or pipe into a desired shape. One type of tube bending machine is the rotary draw bender. This bending machine 5 uses a bending die with a concave groove. The groove is uniform in shape and diameter around the circumference of the die. The bending die has a corresponding counter-die, which combine to form a die set. The forward wall of the counter die has a linear channel that forms a concave groove along its length. This straight groove flushly receives the straight tubular workpiece. The diameter of the groove of the bending die is the same as its corresponding counter die, and both die can have a circular or slightly elliptical shape. The diameter of the grooves of a die set match the outside diameter of the tubular workpiece that they will bend.
A rotary draw tube bending machine 5 with a hydraulic drive is shown in FIG. 1. One drive cylinder rotates a spindle carrying the bending die. The other drive cylinder simultaneously rotates an arm carrying the counter-die. The cylinders extend during a bending cycle, and retract in a return cycle to bring the machine back to its home position shown in FIG. 1. The machine 5 simultaneously distributes pressurized hydraulic fluid to one end of each cylinder during the bending cycle, and to the other end of each cylinder during the return cycle. The pressure delivered to each cylinder is kept equal by mechanical fluid pressure splitting devices 6, and a number of supply, return and pressure balancing hoses 7. Equal pressure in the drive cylinders is important to ensure that both cylinders are extended at the same rate, and are contracted at the same rate.
The bending machine 5 uses a mounting assembly 8 to hold the counter-die. The assembly 8 has two downwardly extending bolts that are received by spaced holes 9 drilled into the top of the rotating arm. The posts are inserted into selected holes 9 to fix the assembly 8 in place, and position the counter-die with the bending die. For example, a hole 9 drilled at a location for a bending die made to form a two inch bend radius into a one inch diameter ASTM schedule 40 pipe, would be about one inch away from another hole 9 drilled for a bending die made to form a three inch bend radius into a one inch diameter schedule 40 pipe. The mounting assembly includes a pivot post and swing assembly to swing the counter-die into and out of engagement with the bending die. Swinging the counter-die out of engagement allows a straight workpiece 10 to be loaded, or a bent workpiece 15 to be unloaded. The machine 5 also includes a bend angle setting device with a protractor-like dial and a stop switch. The switch automatically deactivates the hydraulic drive when the machine reaches the desired pre-set bend angle.
An unbent workpiece 10 is loaded into the bending machine 5 by placing it in an outer concave groove of the bending die. The outer wall 12 of the workpiece 10 flushly engages the concave groove of the die. The straight workpiece 10 is tangent to the circular bending die. The bending die has a hook that engages the opposite side of the tubular workpiece to secure it to the bending die. The counter die and mounting assembly 8 are picked up and set onto the rotating arm with its posts mating selected holes 9 to set the die gap for the particular die set. The counter-die is then swung into pressing engagement with the workpiece 10 to fix the workpiece to the bending die via its hook. When the bending die is rotated, the tube 10 is drawn by the hook, pulled through the channel of the counter die, and wrapped around the groove of the bending die.
The combined rotation of the bending die and rotating arm determines the bend angle of the tube 15. The shape of the bend 16 is determined by the radius of the bending die, the shapes of the arcuate grooves of both dies, and the gap between the dies during the bending process. The groove of a typical bending die has a semi circle shape. The groove of the counter-die has an engineered shape that is slightly elliptical and slightly less than a semi-circle. The edges of the counter-die do not directly contact the edges of the bending die when they are brought together to hold and substantially surround the workpiece 10. The edges of the dies are spaced apart to form a die gap of about ⅛ inch.
The die gap must be properly set to attain a desired bend shape that is free from irregularities in the bend region 16. The bend region 16 of the tube or pipe 15 should have a continuous bend, a desired uniform radius, and a rounded outer portion 17. The die gap determines the amount of pressure the counter-die exerts on the tube 10 during the bending operation. If the gripping pressure is too high, the tube 10 will bind with the counter-die, and slide through the hook during the bending process. A properly set die gap prevents slipping. Slipping results in the tube sliding through the hook and bending die groove, disengages from the bending die, and forms a kink in the tube. This kinking creates a non-continuous bend with a non-uniform radius, which is visually and dimensionally unacceptable, so that the tube has to be scrapped.
The die gap ensures that the groove surface of the counter-die remains flushly engaged with the outer surface 12 of the tube or pipe 10 when forming the bend. During the bending process, the rounded outer portion 17 of the workpiece 10 should conform to the shape of the counter-die, even when the groove surface is slightly elliptical as shown in FIG. 3. This flush engagement is particularly important toward the working end of the counter-die where the metal flow occurs to form the bend. The flow area 19 is a narrow strip located just inside the trailing end of the counter die. When the die gap is properly set, the counter-die provides enough pressure to maintain the tube 10 in flush engagement with the counter-die in the flow area 19 so that the outer half 17 of bend 16 has a desired rounded shape as shown in FIG. 3. If the die gap is too large and the counter-die pressure is too small, the outer wall 12 of the tube or pipe 10 will pull away from the counter-die groove, which causes the outer half 17 of the bend 16 to flatten out 18 as shown in FIG. 4. Third, the die gap also avoids rubbing between the dies, which can lead to wear and tear on the dies and cause binding problems during the bending process.
Conventional tube bending machines should accommodate various dies and die sets, such as those shown in FIG. 2. A tube or pipe workpiece 10 with a particular diameter requires a particular die set. As noted above, the selected bending die and counter-die should flushly engage the outside wall or surface 12 of a tubular workpiece 10 during the bending process. A smaller diameter workpiece 10 requires a bending die and a counter die with smaller concave groove surfaces. A larger diameter workpiece 10 requires dies with larger concave groove surfaces. A particular desired bend radius requires a particular bending die. A small radius bending die produces a tube 15 with a small radius bend. A large radius bending die produces a tube 15 with a large radius bend. Die sets are changed at a job site when the diameter of the tube or workpiece 10 changes. Bending dies are changed at a job site to change the bend radius being formed into a workpiece 10.
A problem with conventional tube bending machines is that they only form a limited number of bends. The machines are specifically designed and manufactured for use with a limited number of bending dies and die sets, and thus only accommodate certain diameter tubes or pipes 10, and only form specific bend radii in those tubes and pipes. For example, the spaced linear holes 9 in the rotating arm of the rotary draw tube bending machine 5 shown in FIG. 1 only allow proper positioning of a limited number of bending dies and die sets, to form a limited number of bend radii in specific diameter workpieces. The location of each hole 9 for securing the mounting assembly 8 and its counter-die is determined prior to manufacture. Once the counter-die assembly is secured in place via a selected set of holes 9, the counter-die location is fixed. Yet, industries are constantly requiring more and more variations in bend geometry and pipe diameters. Conventional tube benders do not meet the industry need for continuously increasing flexibility in permissible workpiece sizes and bend geometries.
Another problem with conventional tube bending machines is that they do not allow field operators to adjust the die gap, such as to allow for variations in workpiece diameter. Although field operators may try to bend workpieces with a slightly different diameter than the bending machine was made, these slight changes in diameter can have a significantly negative affect on the shape and quality of the bends being formed. The workpiece can slip if the gripping pressure is reduced, or bind, break or increase wear if the workpiece is gripped too tight.
A further problem with conventional tube bending machine is its cost and difficulty to repair. Although some tube bending machines provide a hand wheel and screw assembly for setting the die gap, these machines are much more expensive. The cost of the wheel and screw assembly is significant. The wheel and screw assembly also requires a device such as a numerical counter so that the operator can repeatedly return the counter-die to the same desired position each time for repeating a particular bend on many workpieces. The operator must remember to write down the desired positioning number so that the wheel can be returned to this position each time. If the operator forgets to write down the positioning number, then they will not be able to accurately repeat the bend on a new workpiece. In addition, any damage to or wear and tear on this assembly requires immediate repair. Yet, this assembly is time consuming to remove and replace, and because of its significant cost, replacement parts are difficult to obtain, all of which leads to costly down time.
A still further problem with conventional rotary draw bending machines is operating efficiency and safety. During operation, a worker is constantly handling straight and bent pieces of tubing or piping. Straight tube must be properly placed in the machine by hand, and the bent tube must be removed from the machine by hand. Control switches are also operated by hand. Machine efficiency is reduced because a person can only reliably do one of these tasks at a time. The control switches also require the operator to be close to the machine to start and stop a bend. The worker must get close to the machine to turn it off even if something is noticeably wrong, such as a workpiece is binding, which could suddenly release in a snapping motion and injure the worker.
A still further problem with conventional rotary draw bending machines is their many hydraulic hoses. A variety of hoses are needed to balance the pressure and flow rate of the hydraulic fluid to the drive cylinders so that the drive rods extend symmetrically at the same rate. These hoses are not protected and can be easily crushed, punctured, cut or otherwise damaged in a busy construction site or manufacturing setting. The flex hoses also require many connections that can loosen or leak. Yet, hydraulic fluid leaks are both messy and lead to dangerous and slippery work conditions.
A still further problem with conventional tube bending machines is die change over time. Dies are frequently changed during operation. Yet, the dies on many machines are difficult and time consuming to change. Many conventional tube bending machines typically require special tools or the removal of several parts to change either the bending die or the counter die. Accordingly, a significant down time occurs each time a different radius bend is formed or a different diameter workpiece is loaded. Moreover, should a part that needs to be removed to change a die become jammed, stripped or damaged, the entire machine may become inoperable until it is repaired.
A still further problem with conventional tube bending machines is that they are bulky and difficult to move. A worker performing a project in a specific area of a construction site or manufacturing plant may have to haul large quantities of bulky, heavy tubing or pipe from one end of the site or plant to the other and back in order to perform his or her job. This is not only an unproductive use of work time, but can result in injury to the workers.
The present invention is intended to solve these and other problems.